In a solar-passive house, do clear-story windows trap much heat?
How about overcast days?

The graph above shows records of temperature for two days in mid-winter. Records of cloud cover (plotted in purple) show that the first day was overcast and the second mainly sunny.
Through the sunny second day, the temperature readings taken just inside the clear-story windows (black) rose and fell just like the outdoor temperature (red), but they were much higher. I have drawn a dotted red line at a temperature 13.5° higher than outdoors. It fits well to the clear-story temperature (black) on that day. During the previous day, which was overcast, the dotted red line does not fit. It is about 6° higher than the actual clear-story temperature.
By experiment, I found that I could make a model (plotted in green) that would match the actual clear-story temperature as the cloud cover changed. As well as adding 13.5° to the outdoor temperature, I subtracted two thirds of the cloud cover measured in octas. As plotted (green), this model matches the clear-story temperature through both days. At two data points there was a mis-match: those points have not been plotted.

The second graph shows all five days of the experiment. My model of temperature in the clear-story space (plotted green), fits the actual readings (black) on all days.
The model includes one other feature: the maximum temperature that I allow is 26°. That also matches. As mentioned in Part III, a thermostat turns on fans at 26°. That prevented the temperature from rising higher.

Comment

A solar passive house is likely to gain more winter heat if it has north-facing windows in a clear-story above room level. It may also lose more heat. If so, the cost of the clear-story design may not be justified.
This experiment shows that, in this particular house during one harsh winter, the clear-story performed very well.

People may be as surprised as I was at the closely-matching pattern of outdoor and clear-story temperatures in mid-winter, and at how very much warmer the clearstory was: more than thirteen degrees warmer in fine weather.
It may also provoke some thought that the match persisted in overcast weather, but with the clearstory being only eight degrees warmer than outdoors in that case.

Despite more cloud, September was even more arid than August. Weekly temperatures remained normal until the last week, which was remarkably warm. There were some notable events. The 13th, the first 30°-day of the season, was followed by a day more than 16° cooler. Extremely low humidity early on the 20th made the dew point (-8.8°) almost as low as the record set last month. Among minimum overnight temperatures that were near zero, the one on the 24th (22.8°) set a record by being 14.7° higher than normal.
The number of frosts (below +2.2° in the screen) was 13 (a September record), almost as many as in August. Perhaps the frost on the 20th was the last of the season. That is the normal date for it.
There was 5.2 mm of rain on the 14th, and an estimated 0.3 mm on the 29th. (The automatic gauge at the Museum was down by then.)

Comparing September months

The mean daily maximum of 25.0° was rather high, fully 5° higher than last year. With a mean daily minimum (5.7°) that was rather low, the daily temperature range reached the record wide value of 19.3°.
Extremely dry air was shown by a mean early-morning dew point of 2.7°, the lowest September value, 8.1° below normal.
The total rainfall of 5.5 mm (estimated) was very far below the September average (41 mm), at the 8th percentile. That is a serious rainfall shortage. The current rainfall totals for four months (95 mm) and for six months (175 mm) are also serious rainfall shortages. Even worse are the totals for two months (19 mm) and for three months (33 mm): they are severe rainfall shortages.
Similar severe shortages occurred in October 2013, May 2008, and May 2005. Extreme shortages last occurred in the six-month drought of 2002.

Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312. These reports use that rainfall data when it is available. The gauge last reported on 24 September 2017.

All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

A year ago, I showed that Manilla was far from being in a drought. That is not true now. There are severe shortages of rain.

The first graph has rainfall totals up the left margin. They are not expressed in millimetres but as percentile values, Along the bottom margin is the number of months included in calculating each rainfall total.

On the graph, I have compared the rainfall situation today, September 2017, plotted in red with that of September 2016, plotted in grey. Much has changed.

Take, for example, the 12-month (one-year) rainfall total. Rainfall totals for 12 month periods are directly above the value “12” at the bottom of the graph, near the label “Number of Months included”. In data for the month of September 2016 (grey), the 12-month total (actually 802 mm) had been at the 80th percentile, which was very high. In up-to-date data for the month of September 2017 (red), the 12-month total (actually 484 mm) is at the 17th percentile, which is very low.
Although rainfall totals for periods longer than 12 months have not fallen so much, nearly all of them have fallen. Three that have not are those for 30 months, 36 months and 42 months. They were already low, due to including in them some months of low rainfall several years ago, in 2013 and 2014.

So far, real shortages have occurred mainly within the last 12 months. Beyond that, the two-year rainfall total of 1285 mm, for example, is still near normal, plotting at the 48th percentile.

The second graph shows in detail how shortages that are serious or severe have developed during the last six months. These were the monthly rainfall amounts, with the normal amounts in brackets:

As a result, the current situation is as shown below. There are already severe rainfall shortages, at the 2nd or 3rd percentile, in the two-month and three-month totals to date. There are also serious shortages, at the 8th and 9th percentiles, in the four-month and six-month totals to date.

I will update these graphs each month to show how the situation changes.

More arid

September raw anomaly data (orange)

In September 2017 all moisture indicators except cloudiness showed even greater aridity (high up on the graphs) than in August. Daily maximum temperature anomaly (x-axis in all graphs) had now risen very high, but that of the subsoil (lower right graph) had fallen. Daily minimum temperature anomaly (lower left graph) remained extremely low.

Fully smoothed data (red)

The latest fully-smoothed data point is that for March 2017.
At that time, the climate was warm and almost static, after a minor peak in aridity. Although later anomaly values (only partially smoothed) are subject to noise, three of them have raced away towards aridity: dew point fell, daily temperature range rose, and daily minimum temperature fell.

Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

* Normal values for rainfall are based on averages for the 125 years beginning 1883.

This winter had remarkably dry air. The lowest early morning dew point was -10.0°, and the winter mean was -0.5°. Both were record low values. Through the season, the dew point got further and further below the early morning temperature, ending five degrees lower.

Daily maximum and minimum temperatures were near normal. However, they were more than a degree cooler than in the recent winters of 2009 and 2013.

With dry air came a wide daily temperature range of 16.3°, second only to 17.5° in the winter of 2002. It also brought sunny weather, with only 32% cloudy mornings. While that was near the average for my “normal” decade 1999-2008, it was lower than in any recent winter. The winters of the last decade, 2007-2016, were much more cloudy, averaging 45% cloudy mornings. Winter 2016 had 53%!

There were four brief spells of rain this winter, none with heavy rain. They were spaced about seventeen days apart. That sequence had begun in autumn, with heavier falls then. After the 4th of August there was no rain at all.

The total rainfall of 89.8 mm was at the 27th percentile, well below the winter average of 125 mm. Five recent winters had similar amounts of rain: 2000 (98 mm), 2001 (107 mm), 2003 (102 mm), 2004 (97 mm) and 2006 (104 mm). Two were much drier: 2002 (44 mm) and 2011 (55 mm).

Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312. These reports use that rainfall data when it is available. All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

Very few days in August were cloudy, and only one day, the 4th, had some rain: 13.6 mm. Extremely dry air produced a 21st-century record low dew point of minus 10.0 degrees on the 20th. The dry air and clear skies dried out the soil, and also made for wide ranges of temperature. Twelve days were more than 20° warmer than their nights. The actual temperatures, however, were not extreme. Weekly average temperatures remained normal until falling to 3.3° lower in the final days.
Frosts (below +2.2° in the screen) happened on 17 mornings, just two more than normal.

Comparing August months

Arid August months like this occurred in 2012 and 2013, but not since then. The mean early morning dew points in 2012 (-2.2°) and this time (-2.8°) were record values, far below the normal value of +2.2°. This month was also very sunny, had little rain, and had a daily temperature range of 17.9°, a record for August.
Temperatures were close to normal. The daily maximum (19.8°) was a degree above normal, and the daily minimum (1.9°) was a degree below normal.
The total rainfall of 13.8 mm (20th percentile) was far below the August average (40 mm). Added to the low total for July (13.2 mm), the two-month total is only 27.0 mm, which is at the 6th percentile. That makes it the first serious rainfall shortage of any duration since October 2015, when the 30-month total had been at the 6th percentile. For two-month rainfall totals, there has not been such a shortage since nearly four years ago (September 2013).

Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312. These reports use that rainfall data when it is available. All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

Arid and sunny

August raw anomaly data (orange)

In August 2017 all moisture indicators except rainfall showed even greater aridity (high up on the graphs) than in July. Daily minimum temperature anomaly (lower left graph) fell extremely low, but both the daily maximum temperature anomaly (x-axis in all graphs) and that of subsoil (lower right graph) were just slightly above normal.

Fully smoothed data (red)

Fully-smoothed data points now include summer 2016-17. The daily maximum temperature anomaly peaked in February 2017 at +0.9°, much the same temperature as in the previous two peaks: February 2016 and October 2014. The daily minimum temperature anomaly was just about to peak, but the subsoil temperature anomaly was rising persistently.

Moisture anomaly variables, which had moved strongly towards arid in the spring, peaked in aridity during the summer:

Lowest rainfall, in January, was just 13 mm below normal;
least cloudiness, in February, was still 11% above normal;
lowest dew point, in November, was 1.7° below normal;
widest daily temperature range, in January, was only 0.1° wider than normal.

Although aridity reached peaks, this was not an arid summer. The peak values cited were not far from normal, and the graphs show that more arid times occurred within the previous two years.

Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

* Normal values for rainfall are based on averages for the 125 years beginning 1883.

Recent Posts

Back-dated monthly reports

Monthly and seasonal weather reports for Manilla now extend back more than nine years to June 2007. [Select ARCHIVES for the month following.]
"Manilla 3-year climate trends" graphs and reports extend back to May 2010 as consecutive months. Earlier graphs and reports are accessed in ARCHIVES September 2002, 2004, 2006, and 2008.